Hello,
Usually such errors are related to IP through which you are tying to access is not present in white-listed zone.
Just check if anybody else who is accessing from same location is also facing this issue.
Close the Adobe Campaign console >> Navigate to - C:\Users\<ur_user>\AppData\Roaming\Neolane\NL_5 >> clear all the files and directory except "nlclient_cnx.xml" >> Open AC console now and try login.
Please check the below link and you will get an idea where you are missing:
Failure to connect
Perhaps these can help:
Accessing an external database
Configuring Campaign server
Regards,
Venu